With the reserve of fossil fuel in the earth decreasing, the use of solar power becomes an important trend in energy technology development. Since 1954, the development of solar cells has sustained several generations, where dye-sensitized solar cells (DSSCs) belong to the third generation. The power generating principle of the DSSCs is different from that of conventional silicon-based solar cells using contact of n-type and p-type semiconductors (pn junction). A DSSC is a photoelectrochemical system that uses various chemical reactions to transfer light energy to electrical energy. Compared to other types of solar cells, the greatest advantages of DSSCs are low cost and simply manufacturing process. In addition, the substrate in the DSSC can be made of soft materials so as to cause the DSSC flexible.
A DSSC is composed of a photoelectrode, a counter electrode and electrolyte. Generally, the photoelectrode is photosensitive dye-adsorbed mesoporous TiO2 coated on a fluorine-doped tin oxide (FTO) conductive glass, the counter electrode is a conductive glass coated with a platinum film, and the electrolyte is ionic liquid containing I−/I3− redox couples. By light irradiation, the photosensitive dye on the TiO2 absorbs the light and is excited to inject electrons into the conduction band of the TiO2. The electrons flow to the external circuit from the TiO2 through the FTO glass, and arrive at the Pt electrode. On the Pt electrode, the I3− ion in the electrolyte gets the electrons and is reduced to an I− ion, and the I− ion is oxidized by the positively charged dye molecule. Then, the positively charged dye molecule is reduced to a natural molecule, and another I3− ion is generated to complete an electron conduction circuit. The circuit is repeated continuously to convert the light energy to the electrical energy.
Graphene is a kind of allotrope of carbon, can be considered as a single layer of graphite, and therefore has a unique two-dimensional structure with the thickness of a single atomic layer. In the two-dimensional plane of graphene, carbon atoms are arranged in hexagonal honeycomb structures, where each carbon atom maintains sp2 bond with its three adjacent carbon atoms to produce excellent planar conductivity. In 2004, the team of Novoselov and Geim mechanically peeled out the graphene having the thickness of several atomic layers from graphite. This method is simply and cheap. In addition, the peeled graphene has a carrier concentration up to 1013 cm−2, and a carrier migration rate of 10000 cm2V−1s−1 at room temperature. In addition to electrical properties, the graphene has good optical and heat-transfer characteristics; therefore, it is applicable to many fields or products, such as transistors, photodetectors, transparent conductive films and energy harvesting and/or storage devices.
The Taiwan Patent Application No. 099129474, entitled “Graphene transparent electrode, graphene light emitting diode, and method of fabricating the graphene light emitting diode”, discloses a graphene transparent electrode comprising at least one graphene sheet with a specific diameter.
The Taiwan Patent Application No. 100137740, entitled “Electrode performance enhancement by composite formation with graphene oxide”, discloses an electrode comprising an electronically active material (EAM) in a nanoparticulate form and a matrix having a pyrolization product incorporated with graphene flakes.
The Taiwan Patent Application No. 100146689, entitled “Electrode material for chemical energy storage composed of three phase composite of metal oxide, graphene, and nano-carbon materials” discloses an electrode material includes nano-graphene, a nano-carbon material, and transition metal oxide. The nano-graphene is separated by the nano-carbon material, and the transition metal oxide is deposited on the surfaces of the nano-graphene and the nano-carbon material.
After substantial experiments and persistent research, the applicant has finally conceived an apparatus and method for treating graphene by plasma and the application thereof.